Roughly two-thirds of the electricity generated for industry in the United States is used to power electric motors. Approximately one billion motors are in use in the United States. Electric motors are used for machine tools, pumps, fans, compressors and many other industrial, commercial and residential loads.
Many of these motors are small AC induction motors having die cast aluminum squirrel cage rotors. An operating characteristic of these motors, known as "slip," is generally proportional to the electrical resistance in the rotor. Lower resistance produces lower slip and greater efficiency at load-carrying operating points. The resistance of copper is lower than aluminum. The use of copper in such rotors can increase the efficiency of the motor by 2% of the total input energy. Current manufacturing methods using copper need improvement for success in manufacture of small horsepower motors. Currently, a silver-copper brazing technique is used for large horsepower motors, and this method is expensive and slow and not cost effective for smaller horsepower motors.
Another possible method for making a copper rotor is die casting, but copper die casting requires high operating temperatures, which are higher than those required for aluminum die casting. Furthermore, the dies for copper die casting do not have sufficient life for larger scale production. It is therefore, desirable to use preformed or extruded bars in the rotor, and to join these bars to end rings.